Wilhelm schroter



Unirnn STATES. 'ATENT OFFICE.

WILHELM sonno'rnn, or FRANKFORT-ON-THE-MAIN, GERMANY, ASSIGNOR odesirable.

TO FABRIK TEOHNISGI-IER PAPIERE ARNDT UND TROOST, OF SAME PLACE.

PHOTOGRAPHIC=PRINTING PAPER.

SPECIFICATION forming part of Letters Patent No. 585,452, dated June 29,1897.

Application filed January 3, 1895- To all whom it may concern.-

Be it known that I, WILHELM Sonnornn, merchant,of Frankfort-on-the-Main,Prussia, Germany, have invented new and useful Im- 5 provements in theManufacture of Photographic-Printing Papers, of which the following is aspecification. a

This invention relates to the manufacture of photographic-printingpaper. At the present time there is no heliographic process with silverpaper which operates without a special developing or fixing bath. Onlyiron prints have heretofore been developed in pure cold water by asingle washing operation. Besides the well-known compounds of silver theimproved paper contains also an iron compound which in this combinationperforms a double function. In the first place the compound of an ironsalt and a silver salt appears to be much more permanent than that ofsilver salts alone, and in the second place the iron salt, owing to itsbeing reduced in the light, serves to precipitate silver from the silversalt, and thus produces the picture.

The primary material employed in the production of this improved paperis a paper which contains no chlorin. Use is preferably made of pure ragpaper and also fabric for this purpose. The absence of wood is veryThese materials are soaked with a solution which consists of silvernitrate, iron ammonium citrate, tartaric acid, and preferably, also,gelatin. It has been found that the tartaric acid or the citric acid may5 be dispensed with without giving rise to a very great difference- Thesame is the case with the gelatin. The quantity of the iron salt useddetermines the darkness in tone of the copies obtained. The proportionsin which these materials have heretofore been used and have givenfavorable results are one thousand cubic centimeters of distilled water,eighty to one hundred grams of iron ammonium citrate, twelve to twentygrams of silver nitrate, fifteen to twenty grams of tartaric acid, andten to fifteen grains of gelatin. The paper soaked with this solutionkeeps unchanged for several months in the unexposed state. Exposed tothe light it is five times more sensitive than the ordinary pa- SerialNo. 533,734. (Specimeua) per containing potassium ferricyanid. The partsexposed to the light receive a slightlyyellowish color, which by thewashing in pure water changes to deep brown.

By reason of its very great sensitiveness the improved paper may beemployed in cases where such has not hitherto been possible, especiallyfor printing on rather thick cardboard and for producing negativestencils which may be used directly with the same paper or with papercontaining potassium ferricyanid for the production of positives. Thecopies thus obtained are quite unchangeable in the light after thewashing and do not require any further fixing.

According to what is known regarding the several components of thesolution two operations must take place for forming the copy. In thefirst place a small part of the silver nitrate in the presence of theorganic substances will be directly decomposed in the light and becomecolored. In the second place, and this is evidently the more importantopera tion for imparting color, the iron oxid present is reduced by theexposure to light, in consequence of which metallic silver is thenprecipita'ted from the silver nitrate. The opinion that the twooperations take place in conj unction appears to be supported by thebrown colorof the product obtained.

Although the pictures produced with this improved paper keep very longunder ordinary circumstances, it is advisable in cases where thepictures are liable to be brought into contact with acids or substancescontaining acids to submit themto a fixing operation.

Now what I claim, and desire to secure by Letters Patent, is thefollowing:

1. A process for manufacturing a highlysensitive photographic-printingsheet, which consists in soaking a paper or textile fabric free ofchlorin with a solution of silver nitrate and iron ammonium citrate, towhich is added free tartaric acid to redissolve the precipitated silvercitrate.

2. As a new article of manufacture,ahighlysensitivephotographic-printing sheet herein described and impregnated with amixture of silver nitrate, iron ammonium citrate and free tartaric acid,substantially in the propor- I00 tions described, and having a lightyellow name to this specification in the presence of tint which turnsbrown when exposed to the two subscribing Witnesses. light and becomesyellow againwhen moistened, and becomes darker and brown when WILHELMSCIIROTER' 5 dried and which When fixed by sodium hypo- Witnesses:

sulfite takes a brown tint when dried. CARL ROTTY, In testimony whereofI have signed my JEAN GRUND.

